1. Field
The present disclosure relates to a technology of detecting a failure in an output current sensor in a three-phase inverter system.
2. Related Art
FIG. 3 is a diagram showing the configuration of the motor driving system described in Japanese patent application publication JP-A-2008-22645 (paragraphs [0023] to [0028], FIG. 1 and FIG. 2, etc.).
In FIG. 3, the motor driving system is provided with a DC power supply 101, an inverter 102 in three phases, current sensors 103u, 103v and 103w detecting output currents in the U-, V- and W-phases in the inverter 102, respectively, and a control system 200. The control system 200 is further provided with a current detecting unit 201, a current estimating unit 202, a current sensor failure estimating unit 203 and a control circuit 204. The reference sign M designates a motor.
In a normal operation of the system, the current sensors 103u, 103v and 103w detect the output currents in the U, V and W phases, respectively, of the inverter 102 and the detected outputs of the current sensors 103u, 103v and 103w are provided as detected current values iu, iv and iw in the U, V and W phases, respectively, through the current detecting unit 201. The control circuit 204, on the basis of the detected current values iu, iv and iw, produces switching commands to carry out on-off control of semiconductor switching devices in the inverter 102. This makes the inverter 102 output three-phase AC voltages, each with specified magnitude and frequency to drive the motor M.
The current estimating unit 202, by using an arbitrary selection of two of the detected current values iu, iv and iw outputted from the current detecting unit 201, for example, the detected current values iu and iv in the U and V phases, respectively, estimates the remaining detected current value in the W-phase (on the basis of the fact that iu+iv+iw=0, the estimated current value iwa is to be given as iwa=−(iu+iv)) and outputs the estimated current value iwa to the current sensor failure estimating unit 203. By repeatedly carrying out the operation, namely, the selection of detected current values in the arbitrary two phases and the arithmetic operation of the estimated current value in the remained one phase, at a constant period, the detected current values iu, iv and iw and the estimated current values iua, iva and iwa in the U-, V- and W-phases, respectively, are to be successively inputted to the current sensor failure estimating unit 203.
The current sensor failure estimating unit 203, by using a detected current value in one period with respect to one of the three phases, obtains the averaged value of a current value in each phase and, when the averaged value is not zero in a certain phase, makes an assumption that the current sensor in the phase is in failure. When the failure of the current sensor 103w in the W-phase is assumed, for example, such information is sent to the current detecting unit 201, from which the detected current values iu and iv in the U- and V-phases, respectively, except the W-phase are outputted to the control circuit 204. With respect to the W-phase, the estimated current value iwa obtained by the current estimating unit 202 is outputted to the control circuit 204.
By the foregoing operation, the control circuit 204 is to carry out a specified arithmetic processing by using the detected current values iu and iv and the estimated current value iwa and produce the switching commands.
According to the technology described in Japanese patent application publication JP-A-2008-22645, even though a certain current sensor in a certain phase is in failure, the use of the estimated current value in the phase and the detected current values in the other two phases enables the motor M to be driven by the inverter 102 without any problem.
In the related three-phase inverter system, however, current sensors must be provided for three phases, which causes a problem in that the size of the system is enlarged, so as to result in an increase in the cost thereof.
In addition, for the technology of detecting a failure in a current sensor, a technology is known in which two current sensors are used for one phase and detected values of the respective sensors are compared with each other. Such a redundant measure, however, is impossible to avoid an increase in size and an increase in cost like in the foregoing related system.
While, in Japanese Patent No. 5304967 (paragraphs [0005] to [0007], FIG. 1 and FIG. 10, etc.), a technology is disclosed which detects a current in each phase by a so-called semiconductor switching device with a current sense without using any current sensor.
FIG. 4 is a diagram showing the configuration of the motor driving system described in Japanese Patent No. 5304967. In FIG. 4, the motor driving system is provided with an inverter 300 in three phases (U-, V- and W-phases) including semiconductor switching devices 301 through 306 and a capacitor 307, current detecting units 308a, 308b, 310a, 310b, 312a and 312b, adders 309, 311 and 313 and a control circuit 400. Reference sign M designates a motor. For each of the semiconductor switching devices 302, 304 and 306 in their respective lower arms in three phases in the inverter 300, a multi-emitter device is used as a semiconductor switching device with a current sense. The semiconductor switching device with a current sense is provided with a sense emitter and a sense diode.
In the foregoing inverter 300, a current flowing in the sense emitter and a current flowing in the sense diode in the semiconductor switching device 302 in the U-phase are detected by the current detecting unit 308a and the current detecting unit 308b, respectively, and, along with this, the values of the detected currents are added by the adder 309. Moreover, a current flowing in the sense emitter and a current flowing in the sense diode in the semiconductor switching device 304 in the V-phase are detected by the current detecting unit 310a and the current detecting unit 310b, respectively, and, along with this, the values of the detected currents are added by the adder 311. Furthermore, a current flowing in the sense emitter and a current flowing in the sense diode in the semiconductor switching device 306 in the W-phase are detected by the current detecting unit 312a and the current detecting unit 312b, respectively, and, along with this, the values of the detected currents are added by the adder 313. This makes the output current in each phase of the inverter 300 estimated as a discrete sinusoidal wave.